The 68-seat ATR-72 aircraft, registered as VH-FVR, has been grounded in Albury for more than three months awaiting replacement of the horizontal stabiliser, elevator and vertical stabiliser, which provide stability and control to the aircraft.

The grounding came five days after an initial incident on February 20, in which pilots reported moderate turbulence as they approached landing on a flight from Canberra to Sydney.

The ATSB said the pilots advised the engineers that the pitch controls had disconnected, with a possible overspeed. From the onboard equipment, the engineers were able to establish there had not been an overspeed, but that a vertical load factor of 3.34 gravity force was recorded that exceeded the acceptable limit for the aircraft weight.

A flight attendant broke her leg during the incident, and the ATSB report said an engineer had inspected the upper surface of the wing, the rear fuselage and the tail by torchlight that evening for signs of damage, but had not identified any defects and the plane was returned to service the next morning.

The aircraft was then operated for a further 13 sectors over the following days, including a final passenger flight from Sydney to Albury on February 25. The ATSB said on descent to Albury, the aircraft passed close to birds, which alerted the captain to a possibility of a birdstrike.

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"There were no indications that a bird had struck the aircraft, but on the ground, the aircraft's pitch trim fluctuated abnormally," the report said.

The captain alerted the maintenance team to a deformity in the vertical stabiliser which may have been a result of a birdstrike and an engineer was dispatched to inspect the aircraft.

The ATSB said the engineer used scissor-lift equipment to inspect the tailplane and found there was "significant structural damage" on top of the tailplane. The aircraft was grounded for repairs and the ATSB was advised of the situation.

"Later information from the operator suggested that the damage to the tailplane might have been a result of the occurrence involving [the aircraft] on February 20," the ATSB said.

The ATSB interviewed the pilots and engineers and inspected the damaged aircraft at Albury. A final report on the investigation is not due until February next year.

In response to the initial ATSB report, Virgin issued a statement saying the safety of its guests, crew and aircraft was its number one priority as an airline and there were strong protocols in place to ensure the safety of its operations were maintained to the highest standard.

"While this is an isolated issue, we are working with the ATSB, the aircraft manufacturer and our maintenance provider to identify what has occurred," Virgin said. "As the investigation is ongoing, it would be inappropriate for us to comment in any further detail at this stage."

The airline paused growth in its ATR fleet this year, having left an aircraft delivered last September on the ground amid weak demand and talks with the Civil Aviation Safety Authority about improving its procedures after the integration of Perth-based Skywest into its regional arm.

However, Virgin regional head Merren McArthur said this month that she expected the aircraft grounded at Albury to be repaired within a month or so, and for the other grounded aircraft to join the flying fleet within a similar time.

Virgin has deferred the delivery of six more ATR aircraft and Ms McArthur said the timetable would depend on market demand.